Fluorine-containing elastomers, particularly perfluoro elastomers composed mainly of tetrafluoroethylene (TFE) units, exhibit excellent chemical resistance, solvent resistance and heat resistance and therefore are widely used as sealing material under severe conditions.
However, the desired properties have become more severe as technology advances, and in the fields of aerospace, semiconductor manufacturing equipment and chemical plant, sealing properties under high temperatures of 300° C. or higher is desired. Use under such high temperature conditions induce partial degradation of a polymer and cause generation of hydrogen fluoride (HF). Generation of HF at high temperatures not only adversely affects the members that the polymer contacts but is also presumed to adversely affect the elastomer, as HF is aggressive to molecular chains and crosslinking points of the elastomer.
Conventionally, decrease in generation of HF has been attempted by adding silicic acid anhydride (SiO2) to a fluorine-containing elastomer (JP-A-2002-515525). Generation of HF can be sufficiently reduced according to this method. However, because SiO2 contains a large amount of functional groups on the surface, the water content is difficult to control and when a large amount of SiO2 is added, delay in curing of the crosslinking reaction occurs.
In the process of manufacturing a semiconductor, CVD is employed for the step of forming insulating membrane and thin film of metal wiring. In a CVD equipment, elastomeric sealing material is used for sealing various connecting and movable parts. These sealing materials are required not only to have sealing properties, but also to be able to withstand harsh plasma treatment conditions of high-density (1012 to 1013/cm3), as semiconductors are becoming microscopic and substrate wafers are becoming large, and to not contaminate the semiconductor, in which extremely precise processing is required. As an elastomeric material of sealing material that can handle such demands, a crosslinkable fluorine elastomer and silicone elastomer have been employed. Furthermore, in order to achieve mechanical strength more sufficiently than when crosslinked by an elastomer alone, usually an organic or inorganic filler is compounded. Examples of fillers that have been conventionally used or suggested are carbon black, silica (Japanese Patent No. 2783576, Japanese Patent No. 2858198), polytetrafluoroethylene (PTFE) powder, titanium oxide powder, clay, talc and barium sulfate.
In order to clean the chamber of CVD apparatus after the film forming process by CVD, cleaning is conducted by high-density F radical using NF3 remote plasma. As shown in FIG. 1, in a CVD apparatus, remote plasma cleaning is conducted, by connecting another F radical generating machine 1, which can generate high-density F radical, to process chamber 2, in which CVD process is conducted, supplying high-density F radical into chamber 2 and decomposing and removing substances attached to the inside of chamber 2 and sealing material 3. In FIG. 1, numerals 4, 5 and 6 respectively represent a massflow adjuster, a pressure controller and a vacuum pump.
In the process of manufacturing a semiconductor, there is the wet process step, in which the wafer is washed using O3 water. Consequently, the sealing material must be stable to not only NF3 plasma treatment but also O3 treatment.
However, of the above fillers, fillers such as silica and titanium oxide are stable to O3 treatment but are decomposed by NF3 plasma treatment, causing decrease in weight. On the other hand, fillers such as carbon black and PTFE powder are stable to NF3 plasma treatment but are decomposed by O3 treatment, causing decrease in weight. The decrease in weight of the filler that occurs due to the treatments indicates that the decreased matter adversely affects the semiconductor or liquid crystal in some way as unnecessary foreign substances.
As a filler that is stable to these treatments, alumina and an imide filler have been suggested (WO00/64980, WO01/32782). Alumina has resistance to both oxygen plasma and fluorine plasma and has the advantage that the product is not adversely affected even though dust is generated. However, there is the problem that alumina accelerates degradation of a fluorine elastomer under high-density and high temperature fluorine plasma. On the other hand, an imide filler does not generate dust as alumina and does not cause degradation of fluorine rubber as alumina.
In semiconductor equipment including CVD equipment, a switching valve called a gate valve or a slit valve is used for areas at which a wafer is inserted and taken out. The sealing material used in this valve is required to have high strength as the valve suffers mechanical abrasion when opening and closing the valve. However, an elastomer containing an imide filler having the above advantages has low strength, due to large particle size of the filler, and cannot sufficiently withstand the mechanical abrasion when opening and closing the valve. Also, there is the problem that processability of the composition is low, due to large particle size of the filler.
As described above, a fluorine-containing elastomer composition, in which the amount of HF generated under high temperature is small, heat resistance and processability are improved and plasma resistance is excellent, is not yet known.